Switch is still active even when in the “off-state”
Biophysical answers to integrative biological questions
RUB scientists investigate dynamics of signal transmission in cells

In contrast to prevailing assumptions, the switch protein Ras can also transmit signals when in the “off-state.” It is namely not the structure of the protein, i.e. the switch setting, but the binding strength between the proteins involved that is decisive when the information channel is opened. This surprising result was obtained in a German-Israeli collaborative study based on two experimental doctoral theses by Christina Kiel and Daniel Filchtinski (supervised by Prof. Christian Herrmann, Department of Physical Chemistry I at the Ruhr-University Bochum). The results of these studies have been published in the current edition of the Journal of Biological Chemistry.

Binding strength can be manipulated
Specific proteins within human cells transmit information and signals to their destination point. The Ras protein, which switches information channels on and off, is the most important protein. It primarily controls the growth of organisms. Excessive cell growth, which can lead to the development of tumours, can result if the Ras function gets out of control. A paradigm governing the molecular comprehension of the transmission of signals must now be modified due to the results obtained by the research team at the faculty of chemistry and biochemistry. The molecular switch Ras can also transmit signals when in the “off-state.” It is namely not the structure of the protein, but the binding strength between Ras and the partner protein Raf, that is responsible for the opening of an information channel. Prof. Herrmann explained that although the inherent binding strength has a highly specific level, it can nevertheless be artificially manipulated. This implies that it also becomes a focal issue in the development of efficacious agents.

Quantity is decisive
This study also disclosed that former assumptions on the activation mechanism of the partner protein Raf are not valid, but that the structural modifications in the switch protein lead to correlating alterations in the binding partner Raf and to its activation. The improved binding and resultant enrichment of partners such as Raf at specific sites within a cell appears to be the only factor pertinent for information transmission.

Biophysical methods supply an insight
Biophysical methods were primarily found to be the most suitable processes for obtaining the required quantitative insight into the details on the biomolecular interactions and their correlation with biological activity. According to Prof. Hermann, these results are primarily significant for integrative biological research that investigates the complex interaction of almost all components of a living cell on a quantitative basis. This is only possible by determining the strength and dynamics of the interaction as well as the subcellular concentrations of the molecules involved.

International cooperation of young scientists
The report published is based on two theses from the faculty of chemistry and biochemistry, the research work being performed with the assistance of experimental biochemical and biophysical methods. The NMR structure group in Regensburg (supervised by Prof. Hans Robert Kalbitzer) as well as Prof. Gideon Schreiber’s theory research group at the Weizmann Institute (Israel) also made important contributions to this interdisciplinary project. Prof. Herrmann underscored the special significance of the young scientists’ international research and their cooperative work as guests in the partner laboratory in Israel. This collaboration is possible thanks to the German Research Foundation’s collaborative research centre SFB 642, the German Israeli Foundation for Scientific Research & Development, and the Gerhard C. Starck Stiftung, which granted a scholarship for Daniel Filchtinski’s doctorate. The cooperation will be continued and further interesting results are already apparent.

This sketch of a molecular model shows the interaction between the proteins Ras and Raf with an additional inserted branch of a protein component (right-hand side, in the centre), which causes an additional interaction and thus increased binding strength.

As depicted here, the biological activity resulting from an activated information channel correlates with the binding strength between the proteins, and the “off-state” and “on-state” have an overlapping modular range.